Mobile communication services have continuously developed after the 1st generation mobile communication service started around late 1980's providing a low-quality voice communication service primarily under analog cellular standards such as AMPS (advanced mobile phone service). The 2nd generation mobile communication services have provided both an improved voice communication service and a low speed (14.4 Kbps) data communication service under digital cellular standards such as GSM (global system for mobile), CDMA (code division multiple access) or TDMA (time division multiple access). Furthermore, with the advent of the 2.5 generation mobile communication service, a GHz-level frequency band was used and a PCS (personal communications service) has been developed so that a still further improved voice communication service and a still low speed (144 Kbps) data transfer service may be realized.
A mobile communication network for use in up to 2.5 generation mobile communication services includes various communication equipments such as a user terminal, a base station transmitter, a base station controller, a mobile switching center, a HLR (home location register), a VLR (visitor location register), and so forth.
The 3rd generation communication service has been provided in two ways: an asynchronous WCDMA system advocated by 3GPP (generation partnership project); and a synchronous CDMA-2000 system advocated by 3GPP2. Particularly, the WCDMA system is a wireless protocol recommended by IMT-2000, and a great number of communication service operators are now providing or preparing for providing WCDMA services worldwide.
The WCDMA system has advantages of guaranteeing a high speech quality and a great volume of data transmission by using spread spectrum scheme. The WCDMA system adopts a 32 Kbps ADPCM (adaptive differential pulse code modulation) for voice coding and supports a high level of mobility that enables a user to use a voice communication service even while the user moves at a speed of 100 Km per hour. Furthermore, the WCDMA communication method is adopted by the greatest number of countries, and the 3GPP organized by various institutions from South Korea, Europe, Japan, the United States, China, etc., continues to develop technology specifications for the WCDMA services.
Meanwhile, due to the above-described advantages of the WCDMA system, the WCDMA networks have been recently constructed to provide the WCDMA services even in South Korea, the Unites States, China and the like in which the CDMA-2000 services have been fundamentally provided.
Referring to FIG. 1, there is shown a schematic block diagram of a mobile radio communication network capable of providing a WCDMA service in a communication environment in which a CDMA-2000 network is basically constructed.
For the purpose of description, it is assumed that the WCDMA service is offered in some parts within a CDMA-2000 zone 120 in which a CDMA-2000 service is provided. The parts where the WCDMA service is available within the CDMA-2000 zone 120 are referred to as overlay zones 130 and 140. That is to say, a user in the overlay zones can be given either one of the CDMA-2000 service or the WCDMA service selectively. Here, it is obvious that a multimode-multiband (hereinafter, referred to as ‘MM-MB’) terminal is required for both the CDMA-2000 service and the WCDMA service.
MM-MB terminals 110 and 112 support multi modes and multi bands. Here, the multi modes include a synchronous mode, an asynchronous mode, and the like, while the multi bands include the 2nd generation mobile communication services using a frequency band of 800 MHz, the 2.5 generation mobile communication services using a frequency band of 1.8 GHz, the 3rd generation mobile communication services using a frequency band of about 2 GHz and a 4th generation mobile communication service to be provided in the near future. The MM-MB terminals 110 and 112 may be switched to a WCDMA mode, an IMT-2000 mode, or the like, depending on what type of communication service is provided, in the region where they are currently located.
FIG. 2 is a schematic block diagram showing an internal configuration of the prior art MM-MB terminal 110.
The prior art MM-MB terminal 110 includes an RF (radio frequency) antenna 210, an RF transceiver 220, a filter unit 230, a modem unit 240, a controller 250, and so forth.
The RF antenna 210 receives an RF signal transmitted from a neighboring wireless base station. The RF transceiver 220 receives the RF signal from the RF antenna 210, demodulates the received RF signal and sends the demodulated RF signal to the filter unit 230. Further, the RF transceiver 220 modulates transmission data received via the filter unit 230 and the modem unit 240, and transmits the modulated transmission data via the antenna 210, under the control of the controller 250.
The filter unit 230 and the modem unit 240 include a WCDMA filter 232 and a WCDMA modem 242 for the WCDMA service and a CDMA-2000 filter 234 and a CDMA-2000 modem 244 for the CDMA-2000 service, respectively. Depending on an operating mode of the MM-MB terminal 110, the filter unit 230 extracts a desired digital signal from the demodulated RF signal received from the RF transceiver 220, using either one of the WCDMA filter 232 and the CDMA-2000 filter 234, and transfers the extracted digital signal to the modem unit 240. Further, the modem unit 240 processes the digital signal received from the filter unit 230 and takes charge of a call processing according to a protocol defined by WCDMA or CDMA-2000.
The controller 250 controls the overall operation of the MM-MB terminal 110 and allows the MM-MB terminal 100 to operate selectively in either one of the WCDMA mode and the CDMA-2000 mode, depending on what type of the received RF signal is received (i.e., depending on whether the RF signal is a WCDMA signal or a CDMA-2000 signal). Moreover, if a certain operating mode is selected, the controller 250 transmits a control signal to the modem unit 240 to thereby drive one of the WCDMA modem 242 and the DCMA-2000 modem 244 depending on the selected mode.
Meanwhile, in case the MM-MB terminal 110 moves from the overlay zone 130 to the CDMA-2000 zone 120 or from the CDMA-2000 zone 120 to the overlay zone 130, a switching between the WCDMA mode and the CDMA-2000 mode is required. That is, if the MM-MB terminal 110 that has been receiving the WCDMA service in the overlay zone 130 moves into the CDMA-2000 zone 120, the WCDMA mode of the MM-MB terminal 110 should be switched to the CDMA-2000 mode.
As described with reference to FIG. 2, in order to switch the MM-MB terminal 110 from the WCDMA mode to the CDMA-2000 mode, the WCDMA modem 242 under operation should be stopped and the CDMA-2000 modem 244 should be activated instead. Accordingly, in the conventional mobile communication environment, the MM-MB terminal 110 has to get out of the overlay zone 130 completely, i.e., the WCDMA signal has to be no more received, before the CDMA-2000 modem 244 is activated.
However, in the conventional method in which the MM-MB terminal 100 has to get out of the overlay zone 130 and a call has to be completely disconnected with the WCDMA network before the CDMA-2000 modem is activated, it takes about 10 to 15 seconds for the MM-MB terminal 110 to switch its operating mode from the WCDMA mode to the CDMA-2000 mode. Therefore, there occurs a problem that the MM-MB terminal 110 moving from the overlay zone 130 to the CDMA-2000 zone 120 cannot use the mobile communication service at all during a relatively long time ranging from 10 to 15 seconds required to be completely switched to the CDMA-2000 mode.
Even though the above description has been provided for the movement of the MM-MB terminal 110 from the overlay zone 130 into the CDMA-2000 zone, same problem may occur in the reverse case, i.e., when the MM-MB terminal 110 in the CDMA-2000 zone 120 moves into the overlay zone 140.